On the turn I like the check behind with 2/3 pot size left, because only bet that makes sense is a shove which will usually result in being called only with better flushes. On the river, it's close between c/c and c/f. Here it would be nice to have some reads, but in general I don't think villain will raise here worse or bluff too often unless he likes to bluff a lot thus I would pick c/f on the river against unknown.